Signaling to the mechanistic target of rapamycin (mTOR) regulates diverse cellular processes, including protein translation, cellular proliferation, metabolism, and autophagy. Most models place Akt upstream of the mTOR complex, mTORC1; however, in T cells, Akt may not be necessary for mTORC1 activation. We found that the adaptor protein Carma1 [caspase recruitment domain (CARD)–containing membrane-associated protein 1] and at least one of its associated proteins, the paracaspase MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1), were required for optimal activation of mTOR in T cells in response to stimulation of the T cell receptor (TCR) and the co-receptor CD28. However, Bcl10, which binds to Carma1 and MALT1 to form a complex that mediates signals from the TCR to the transcription factor NF-κB (nuclear factor κB), was not required. The catalytic activity of MALT1 was required for the proliferation of stimulated CD4⁺ T cells, but not for early TCR-dependent activation events. Consistent with an effect on mTOR, MALT1 activity was required for the increased metabolic flux in activated CD4⁺ T cells. Together, our data suggest that Carma1 and MALT1 play previously unappreciated roles in the activation of mTOR signaling in T cells after engagement of the TCR.